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AM1806: About Silicon Errata description “2.1.5 System-Level ESD Immunity Usage Note”

Tsurumoto
Genius 11750 points
Part Number: AM1806

Hi,

 

According to the Silicon Errata for AM1806

http://www.tij.co.jp/jp/lit/er/sprz314h/sprz314h.pdf

at chapter  “2.1.5 System-Level ESD Immunity Usage Note”, the following design is recommended.

 

 

However, load current to X1 could be about 12.5mA if the above design is implemented.

12.5mA is too big, and the waveform may become loose.

And also, because of the following condition is satisfied 

     

Voh(out out of X1 High) < Vih(threshold of incoming high to AM1806)



then unexpected behavior could be occurred.

 

Question 1:

Why so little resistance are recommended to R1, R2?



Question 2:

What is the recommended Crystal oscillator for X1?

Best regards,

HaTa.

  • 0
    TI__Guru**** 161600 points

    Hi,

    For question 1:
      I am not sure why such resistor values are recommended, but I know that appropriate validation tests were performed so that the Errata recommendation is made. You should take into account the recommendations in 2.1.5 System-Level ESD Immunity Usage Note.

    As for question 2:
      this is described in Section 6.5 Crystal Oscillatoror  External Clock Input of the Device Datasheet.

    Best Regards,
    Yordan

  • 0
    TI__Guru* 78285 points

    Hi 

    For Q1 

    The circuit in the errata is just a reference that we had tested with our EVMs etc. It seemed to work and was acceptable with the external oscillators available at that time. 

    Customer can choose the values as per their choice of external oscillator and ensure that it meets the CLKIN requirements (1.2V) and is robust against noise etc. 

    The values have to be chosen carefully because

    If the resistance is high, it will be more sensitive to noise. (This is obviously somewhat system design related and will vary from system to system) 

    If the resistance is too low there will be a large voltage drop due to output impedance of the OSC ( I believe this is what your customer is concerned about?) 

    For Q2

    No specific recommendations customer is free to choose the commonly available 3.3V or 1.8V oscillators , but need to ensure that the CLKIN voltage to the device 1.2V +/- tolerance listed in the datasheet.

    Hope this helps/

    Regards

    Mukul